My research objectives involve the application of basic immunochemical techniques to the study of certain problems of clinical medicine. For several years now, I have been engaged in studies with antibodies specific for a variety of low molecular weight substances of biological or clinical importance. The low molecular weight substance toward which my principal effort has been directed is the cardiac glycoside digoxin. Antibodies specific for digoxin have been developed in this laboratory with the hope (as stated in my original 1965 application for this research grant) that these antibodies "may be of value (a) in the immunologic assay of digoxin in plasma and tissue fluids, (b) in the amelioration of clinical digitoxicity, and (c) in the study of the mode of action of digoxin, both in intact animals and in cardiac-muscle preparations in vitro." These antibodies have already been used in the development of a rapid, sensitive and specific radioimmunoassay method for the clinical determination of serum digoxin concentrations in man and have shown to be capable of removing digoxin from cells and of reversing lethal digoxin intoxication in experimental animals. The objectives of my current research are: (1) the application of the digoxin radioimmunoassay method to the study of the clinical pharmacology and biologic availability of this drug; (2) a better characterization of the quantitative aspects and cellular mechanisms involved in the reversal of canine digoxin intoxication, which will enable the use of digoxin-specific antibodies in the reversal of severe digoxin toxicity in man; (3) the use of digoxin-specific antibodies and of digoxin-protein conjugates in the study of the mechanisms of action of digoxin at the cellular level; (4) a study of the unusual metabolic fate of digoxin in immunized animals and an application of the information obtained from this investigation to the study of immunological mechanisms by which immune complex disease may be prevented or reversed; and (5) the development of specific antibodies for the study of other low molecular weight substances of biological or clinical importance.